1867.] ^IR. O. S.VLVIN ON THE BIRDS OF VERAGUA. 131 



The geograjjliical position of the portion of Veragua we are now 

 considering, situated as it is between Panama and Costa Rica, cer- 

 tainly suggests that its ornithological fauna would consist of species 

 belonging to each fauna, with the addition of some few species pecu- 

 liar to the district. Such appears to be actually the case. Rather 

 more than one-half the birds are also found in Costa Rica, while rather 

 less than two-thirds are found on the Panama Railway. About one 

 in ten has not been hitherto seen beyond its limits. Rather less 

 tban three in seven extend beyond Panama into the southern con- 

 tinent of America, while three in seven extend northward into Grua- 

 temala, Mexico, or the northern continent of America. 



These proportions show that this district most resembles the 

 Isthmus of Panama as regards its birds, that it has a less strong affi- 

 nity to Costa Rica, and that out of the wide-ranging species a rather 

 larger proportion belongs to more northern regions than to southern. 

 It would be necessary to compare closely the birds of this district 

 with those of Costa Rica to ascertain accurately where the balance 

 of their relationship lies. The presence of several peculiar forms, 

 such as Cephalopterus, ChasmorhyncJms, Oreopijra, Microchera, 

 &c., suggests that Veragua belongs zoologically to Costa Rica, and 

 that Panama maintains a strictly derivative fauna, and has at no 

 period of the geological history of the isthmus ever been a centre of 

 segregation. On the other hand, it is to Costa Rica and Veragua 

 united that we must look to find the origin of most of the species 

 now found on the Isthmus of Panama, it being evident that this 

 district has for a long period occupied a position as an island, or one 

 of the islands which lay between the two continents at a time when 

 the two oceans were united by two or more channels. It is for geo- 

 logists to tell us where these divisions were situated. An obvious one, 

 separating Costa Rica, Veragua, and Panama from the southern 

 continent, is the line from the Atlantic bay of San Bias across to the 

 mouth of the Bayano on the Pacific. 



Regarding Costa Rica, A'^eragua, and Panama as a whole, there are 

 indications, in the Humming-birds at least, of some separation havino* 

 existed between the extreme ends of the district, Microchera albo- 

 coronata of the southern extremity being represented by M. parvi- 

 rostris at the northern, Chalyhura isaurcB by C. melanorrhoa, 

 Thaiimantias chionurus by 2\ cupreiceps. As no instance of repre- 

 sentative forms occurs in other groups of birds, it is perhaps more 

 probable that the local distribution of particular plants from which 

 these birds take their food limits the range of each race than that 

 any actual geographical barrier has given cause to this divergence. 



I hope shortly to return to this subject in a paper on some col- 

 lections from Costa Rica ; but I may state that my present view is 

 that this district, viz. that included from the rise of the mountains 

 to the northward of the line of the Panama Railway to the southern 

 shore of the lake of Nicaragua and the river San Juan, forms the key 

 to the peculiarities of the Central-American bird-fauna. Previously 

 to the separation indicated between Costa Rica and the southern 

 continent, but when the more northern strait, where the lake of 



